1. Field of the Invention
The present invention relates to a microwave sensor, and more specifically, to a sensor adopting frequency-modulated continuous wave (FMCW) for detecting whether the parking spaces are occupied.
2. Description of the Prior Art
The design of existing indoor parking lot detection sensors mostly adopts infrared as the sensing device. For example, the Taiwan patent no. I333636 disclose a parking space detection sensor for detecting whether a specific parking space is taken based on whether the emitting and receiving of infrared beams through reflecting units are interrupted not or. Please refer to FIG. 9, which shows a schematic diagram of how the existing technology detects a parking space. When the parking space is empty, a light-emitting unit 12 emits infrared beams to a reflecting unit 14 that reflects the beams to a light-sensing unit 16. However, when the parking space is taken by an object standing between the light-emitting unit 12 and light reflecting unit 14, the infrared beams are interrupted and cannot travel from the light-emitting unit 12 to the light reflecting unit 14. Therefore the light-sensing unit 16 cannot detect any infrared beam being reflected.
The existing detecting device makes use of infrared beam sensors, which generally are suitable for an indoor parking lot management system. Given that a fixed distance must be maintained from the light-emitting unit 12 and light-sensing unit 16 to the light reflecting unit 14, the light-emitting unit 12 and light-sensing unit 16 usually sit on overhead installations such as the steel racks of the ceiling or the steel utility pipes in the basement. Therefore, the requirements of overhead installation and reflection angle are limits of the existing technology that adopts infrared beam sensors to detect the availability of a parking space.
Besides, additional overhead installation is needed if the existing infrared beam sensor is to be used in an outdoor parking lot. And, weather conditions, such as rain or heavy fog, or environmental factors, such as dust or sludge, influence the effect of infrared beam detection.
Therefore, it is extremely important to provide a sensor for detecting a parking space not subject to the interference of weather conditions or environmental factors indoors or outdoors.